|Pickled plum (umeboshi) onigiris packed for lunch, separated by grasslike decorations|
One cup of raw rice, when cooked, will make three onigiris. I'll explain how to make just three, and you can extrapolate from there.
Cook the rice as usual.
Sprinkle on a little bit of salt.* Place little bits of filling on your rice like so:
|Soon-to-be onigiris filled with umeboshi|
|Not to soft, not too hard (or so we hope)|
Wrap a couple pieces of onigiri-nori around each triangle, and serve or put in your obento box (packed lunch) for later. If they're for an obento, it's a good idea to put a little something between them to keep them from sticking.
Some filling favorites:
Nothing - just plain rice (That's how Denny likes his.)
Umeboshi (pickled plum)
Tuna and mayonnaise (just enough mayo to hold the tuna together)
Tuna, mayonnaise, and umeboshi
Gyudon-style beef - chop and squeeze out excess moisture
Grilled salmon, crumbled (without bones)
Minced chicken, like that used for Sanshoku-gohan
Or mix your rice before forming with Japanese rice seasonings, like this one made from seaweed and edamame (steamed green soybeans).
If you like seafood, you can use such things as: mentaiko, tarako, katsuobushi (fish flakes) and soy sauce, ikura (salmon roe), seaweed, etc.
If you're mass-producing them, you will probably want to take several onigiris' worth of rice out of the pot and put it on a plate or tray to cool, and work with that rice. You will need to put your fillings in as you go, not like that simple only-three method I explained above.
* Some people prefer to not salt the rice, but wet their hands in salted water when forming the onigiris. Another way is to put out a small dish of salt, and put a little on your dampened hands before shaping the rice balls.